Capacity Control; Demand Limit; Night Mode - Danfoss BW10 020-090 Operation Instructions Manual

The following tables summarise the possible selections
depending on the control types (local, remote or network) and
the following parameters:
• Setpoint select in local control: item LSP_SEL in the
GENUNIT menu permits selection of the active set-point,
if the unit is in local operating type.
• Heating/cooling operating mode.
• Setpoint selection contacts: setpoint selection contact
status.
• Schedule 2 status: schedule for setpoint selection.
LOCAL OPERATING MODE
PARAMETER STATUS
Heating/cooling Local setpoint
operating mode selection
Cooling sp 1
Cooling sp 2
Cooling Ice_sp
Cooling auto
Cooling auto
Heating sp1
Heating sp 2
Heating sp 3
Heating auto
Heating auto
REMOTE OPERATING MODE
PARAMETER STATUS
Heating/cooling Setpoint selection
operating mode contact
Cooling sp 1 (open)
Cooling sp 2 (closed)
Heating sp 1 (open)
Heating sp 2 (closed)
5.5.2 - Reset
Reset means that the active setpoint is modified so that the
machine capacity required is adjusted to be as close as possible
to the demand. This modification is in general a reaction to a
drop in the load. For the control system, the source of the reset
can be configured in the HCCONFIG configuration: it can be
provided either by the outdoor temperature (that gives a
measure of the load trends for the building) or by the return
water temperature (heat exchanger delta T, gives an average
building load).
In response to a drop in the outdoor temperature or to a drop in
delta T, the cooling setpoint is normally reset upwards in order
to optimise unit performance:
In both cases the reset parameters, i.e. slope, source and
maximum value, are configurable in the RESETCFG menu (see
section 4.3.8). Reset is a linear function based on three
parameters.
• A reference at which reset is zero (outdoor temperature or
delta T - no reset value).
• A reference at which reset is maximum (outdoor
temperature or delta T - full reset value).
• The maximum reset value.
18
Time schedule 2 Active setpoint
status
- Cooling setpoint 1
- Cooling setpoint 2
- Ice storage cooling
setpoint
occupied Cooling setpoint 1
unoccupied Cooling setpoint 2
- Heating setpoint 1
- Heating setpoint 2
- Heating setpoint 3
occupied Heating setpoint 1
unoccupied Heating setpoint 2
Active setpoint
Cooling setpoint 1
Cooling setpoint 2
Heating setpoint 1
Heating setpoint 2
Reset example in cooling mode based on the outside
temperature
Outdoor temperature (OAT)
Heat exchanger delta T
Legend
A Maximum reset value
B OAT or delta T for no reset
C OAT or delta T for full reset
D Building Load

5.6 - Capacity control

This function adjusts the number of active compressors to keep
the heat exchanger water temperature at its setpoint. The
precision with which this is achieved depends on the capacity
of the water loop, the flow rate, the load, and the number of
stages available on the unit. The control system continuously
takes account of the temperature error with respect to the
setpoint, as well as the rate of change in this error and the
difference between entering and leaving water temperatures, in
order to determine the optimum moment at which to add or
withdraw a capacity stage.
If the same compressor undergoes too many starts (per hour) or
runs below one minute each time it is started this automatically
brings about reduction of compressor starts, which makes
leaving water temperature control less precise.
The high pressure, low pressure or defrost unloading func-tions
can also affect temperature control accuracy. Compres-sors are
started and stopped in a sequence designed to equalise the
number of start-ups (value weighted by their operating time).

5.7 - Demand limit

The demand limit is used to restrict the unit power consumption.
The control system allows limitation of the unit capacity, using
user-controlled volt-free contacts.
The unit capacity can never exceed the limit setpoint activated
by these contacts. The limit setpoints can be modified in the
SETPOINT menu.

5.8 - Night mode

The night period is defined (see GENUNIT configuration) by a
start time and an end time that are the same for each day of the
week. During the night period the unit capacity may be limited.